The invention relates to a crankshaft for an internal-combustion engine and, more particularly, to a crankshaft having webs with recesses.
German Patent Document DE-OS 36 14 722 shows a crankshaft for an internal-combustion engine having crankshaft webs with recesses on each side. These recesses are arranged such that a maximal web thickness remains in the overlapping area of the journal and the crank pin.
It is an object of the present invention to provide a crankshaft which ensures improved flexural and torsional loads while optimizing mass compensation.
This object has been achieved in accordance with the present invention by providing recesses molded into the crankshaft webs in each case symmetrically with respect to a vertical longitudinal center plane oppositely inside a clear outer contour of the crankshaft webs which, in the area of the recesses, are constructed as a profile with side legs which has a U-shaped cross section. A reinforcing rib is arranged between the recesses of the crankshaft webs which are arranged above one another, in the overlapping area of the crank pins and the journals.
Principal advantages achieved by the present invention are that, as a result of the recesses arranged in each crankshaft web in a targeted manner, a weight reduction is made possible with effective mass compensation. In particular, the recesses are arranged above one another such that, in the endangered area of each crankshaft web, despite the maximally large recesses, a cross-section is built up which is as large as possible to absorb the flexural and torsional load in a defined manner.
In each crankshaft web, the recesses form a U-profile which is aligned in the longitudinal planes of the web and which promotes an optimal torsional and flexural load in the most endangered zone.
The large cross-section between the two recesses is achieved by a reinforcing rib which has its highest elevation in the area of the overlapping between the journal and the crank pin.
The construction of the recesses, or their shape and size, may differ according to the constructive circumstances in the directly opposite crankshaft webs. Thus, it is advantageous for the recesses to be relatively large in the area of the crank pin so that the rotating mass part is reduced which results in a more favorable mass compensation while the weight is reduced at the same time. In the case of a 4-cylinder crankshaft, without laid-in cores, these measures can be carried out simply as a cast part and a forged part.
The opening angle of the counterweight of the crankshaft web may be calculated corresponding to the rotating mass. The opening angle of the counterweight of the crankshaft web is optimized with respect to a relative optimum for a minimal weight with a maximally possible mass compensation. With respect to an angle of 180.degree., the values for the ideal angle are at 19.4% weight reduction and 4.6% unbalance loss.